GHSA-2xgg-2x8h-8xw4

### Summary

Kimai 2.56.0 contains an authenticated improper authorization vulnerability in the Web rate editing flows for projects, customers, and activities. A user who can edit one authorized parent object can combine that authorized parent ID with the rate ID of a different, unauthorized parent object and thereby modify the unauthorized rate record.

This affects `ProjectRate`, `CustomerRate`, and `ActivityRate` editing. The issue is caused by missing parent-child consistency validation and allows cross-project, cross-customer, or cross-activity tampering of billing-related configuration.

### Details

The issue affects the following Web routes:

- `GET/POST /en/admin/project/{id}/rate/{rate}` - `GET/POST /en/admin/customer/{id}/rate/{rate}` - `GET/POST /en/admin/activity/{id}/rate/{rate}`

In both cases, the parent object and the rate object are resolved independently from user-controlled route parameters. The controller only checks whether the current user may edit the parent object referenced by `{id}`, but it does not verify that the child rate object referenced by `{rate}` actually belongs to that same parent.

In these controllers, there is no validation such as:

- `$rate->getProject() === $project` - `$rate->getCustomer() === $customer` - `$rate->getActivity() === $activity`

This missing binding check is especially notable because the API delete endpoints already enforce the expected parent-child relationship.

This shows that parent-child consistency is already a recognized invariant in the application design, but the Web edit endpoints fail to enforce it for projects, customers, and activities.

*A PoC was provided, but removed for security reasons.*

### Impact

This vulnerability allows authenticated users to tamper with billing-related rate configuration outside their authorized project, customer, or activity scope. An attacker can modify rate values belonging to other teams or business domains, which can affect time-based settlement, inherited pricing, cost calculations, budget reporting, revenue reporting, and downstream invoice generation.

Because the issue directly persists changes into `kimai2_projects_rates`, `kimai2_customers_rates`, and `kimai2_activities_rates`, it is a real cross-scope integrity vulnerability rather than a UI-only flaw. The attack breaks team-based isolation boundaries for high-value financial configuration.

# Solution

The rate edit forms for `customers`, `projects` and `activities` now verify that the rate belongs to the parent referenced in the URL and reject the request otherwise.

See [https://www.kimai.org/en/security/ghsa-2xgg-2x8h-8xw4](https://www.kimai.org/en/security/ghsa-2xgg-2x8h-8xw4) for more information.